Heat pump



J. S. PALMER Nov. 17, 1964 HEAT PUMP Filed Nov. 30,

BUILDING WALL AIR TO BUILDING REGISTERS ill FIG.

FIG- 2.

I INVENTOR. JEWELL S. PALMER ATTORNEY.

United States Patent 3,157,227 HEAT PUB/[P lewell S. Palmer, Eaytown,Tex, assignor, by mesne assignments, to Essa Research and Engineering6on1 pany, Elizabeth, Null, a corporation of Delaware Filed Nov. 30,1951,Ser.No. 155,952 1 (Ilairn. (El. 165-29} The present inventionrelates to a method and apparatus for improving the performance of heatpumps during cold-Weather operation. More particularly, the presentinvention relates to improvement of efficiency of heat pumps whichcomprise a compressor, an evaporative coil, and a condensing coil byproviding a source of heat for said evaporative coil during use of saidheat pump at low temperatures.

The heat pump has obtained broad recognition as a year-around source ofair conditioning, providing cooling in the summer and heating in thewinter. These heat pumps operate on a closed cycle, compression basedrefrigeration system which includes a compressor, an evaporative coil, acondensing coil, and a refrigerant. in the operation of these heatpumps, the refrigerant is compressed, liquefied by heat exchange with anair current which is thereby heated, and the liquefied refrigerant isallowed to vaporize through a choke valve into an evaporative coil whichis contacted by a second stream of air which is thereby cooled. Theevaporated refrigerant is recycled through the compressor forliquefaction and a repetition of the above-described process. Theheating capacity of a heat pump is sensitive to ambient temperatureconditions, falling off rapidly with lower ambient temperatures. This isdue to the decrease in temperature diilerential between the air passingacross the evaporative coil and the temperature of the liquid vaporizingtherewithin. In the prior art, for operation at extremely lowtemperatures, it has been necessary to supplement the heat pump with anelectric resistance heater placed in the stream of air circulated insidethe building being heated,

or to utilize gas heaters placed within the building and normally ventedto the atmosphere because of building code requirements. Eitheralternative is an expensive expedient in that electrical energy is anexpensive source of heat in most areas, and the requirement of ventingfor gas heaters placed within inhabited buildings involves a great lossof heat in .flue gas which is exhausted to the atmosphere.

The present invention obviates the use of these supplementheating meansWithin the building being heated by providing heating means for theevaporative coil of the heat pump. This source of heat may be a gas oroil burner, the exhaust gases from a gasoline-driven engine used tooperate the compressor of the heat pump, circulating water from thejacket of such gasoline engine, exhaust steam from a steam engine usedto drive the compressor, including turbine-driven compressors which arethemselves driven by steam, or any other source of heat which may beavailable for use.

By the practice of the present invention, all combustible fuels may bekept out of the space being heated,

thereby complying with building code requirements and providing safeoperation while avoiding losses or" heat due to venting of line gases.Further, during the operation of a heat pump at low temperatures, it hasfrequently been necessary to make provision for defrosting theevaporative coil periodically in order to remove condensed and frozenmoisture which collects upon these coils during the heating cycle. Bythe practice of the present invention, such provisions for defrostingare no longer necessary and the entire defrosting concept can beeliminated. 1

In the use of the present invention, wherein substanti-- "ice ally totalrecycle of the heated gases within the evaporator housing is utilized,heat losses are minimized and approach those of gas fired space heatersutilized without venting. Thus, although nonvented space heaters areforbidden by ordinance in most cities, the eliiciency associated withnonvented space heaters may still be obtained by using a heat pumpmodified in accordance with the present invention. Thus, it is apparentthat the heat pump, by incorporating the present invention, is madepractical for use in even the most extreme of cold climates rather thanbeing limited to mild climates as is presently the case.

As an indication of the diminution of heating capacity in a commercialheat pump as the ambient temperature declines, the following informationset forth in Table I relates the heating capacity and compressor wattsto the ambient temperature at which the heat pump is operating:

T able I Outdoor Temperature, degrees Heating Compressor Capacity WattsIn order to illustrate more fully the concept of the present invention,reference is directed to the drawings wherein:

FIG. 1 is a representation of a split-unit heat pump wherein thecompressor and one coil are located outside the building being heatedduring the winter and cooled during the summer; and

FIG. 2 is a schematic representation of an automatic control system foroperating the valves to insure full recycle of the air within the coilhousing in response to the temperature of the ambient air.

Referring now to FIG. 1, there is schematically set forth a heat pumputilizing the present invention. In PEG. 1 the heat pump is made up of acompressor ltltl communicating by way of line 1&1, four-way valve 102,

and line 193 with a condensing coil 1% wherein heat is transferred tothe air flowing Within a building duct 146 by means representedschematically by fan 1 95. Coolant is passed from the condensing coil104 by Way of line 1% into an evaporating coil 1% and from thence by Wayof line 107 and four-way valve 1% into line 1&8

for return .into the compressor 1%. The compressor 1% is shown as beingdriven by an internal combustion engine 111 although it might suitablybe driven by an electric motor, a steam engine, a steam turbine, orother motive means. The evaporating coil 1% is shown as being placedWithin a housing 111, comprising an air inlet 112 controlledby valve113, the air being passed through the housing and over the evaporativecoil 1% by means of fan 114. The air is passed from the housing by Wayof outlet 115. Recycle duct means 116 are provided whereby during verylow temperature operation, the valve 113 may be substantially closed andvalve ll! which serves both outlet 115 and recycle duct 116 issubstantially closed, leaving only so much clearance as isrequired forthe circulation through the housing 111 of sufficient oxygen to supportcombustion when a gas or fuel oil fired flame is used as a source ofheat. During cold temperature operations, the cooling Water from theinternal combustion engine 110 is circulated by Way of lines 120 and121, pump 122 and line 123 to a heat transfer radiator 124 within thehousing and in the path of circulating air before it contacts theevaporative coil 1%.

The cooling water is returned by way of line 125 into the jacket of theengine 110. During summer operations when the additional heat is notdesired, or in winter but when the heat load on the heat pump is lessthan its capacity at ambient temperatures, all or a portion of the watermay be circulated through external radiator 127 for providing sutlicientcooling for the internal combustion engine. The amount of watercirculated through the radiator 124 may be controlled by a heatresponsive element 129 which actuates a valve 130 within the circulatingwater line in order to control the amount of heat delivered to theinside of housing 111. Supplementary to the circulating water from theinternal combustion engine, where the amount of heat abstracted from thecirculating water is insufficient, a burner 132 is supplied with gas byway of line 133 controlled by valve 134. The valve 134 is controlled bya temperature responsive element 129 similar to the manner in whichvalve 130 is controlled. The amount of heat supplied by the gas burner132 may supplement the heat available from the engine 110 or may be inlieu of the circulating water source above described.

During cold weather operation, assuming that the gas burner is necessaryto provide at least a portion of the heat required, the valves 113 and117 are moved to the dotted line position shown in FIG. 1, under whichcondition the air circulated through the housing 111 will be sufiicientonly to supply the oxygen needed for combustion of the gas burned, and apartial recycle stream of air is provided. It should be noted that whenthe heat supplied by the circulating water from the motor 110 issufiicient to supply the heat load for the heat pump, the valves 113 and117 may be completely closed, resulting in a full recycle of air withinthe housing 111.

Under these conditions, the heat pump operates merely as a means fortransferring heat from the gas burner or internal combustion motor intothe building to be heated. Since the housing 111 normally will besupplied with insulation, the amount of the heat lost into theatmosphere is negligible and is comparable in degree to the minor heatlosses which are experienced with the use of space heaters not vented tothe atmosphere. Thus, the advantages of a nonvented space heater areobtained without the danger of suffocation or asphyxiation of personswithin the building being heated, and in full compliance with cityordinances. Further, defrosting of the evaporative coil is no longerrequired.

It should be recognized that when a steam-driven prime mover is usedinstead of the internal combustion engine 110, exhaust steam may becirculated through the radiator 124 for supplying heat to the heat pump.Likewise, where an electrical prime mover is used instead of engine 110,the gas burner 132 will provide all of the heat for the heat pump. andthe valves 117 and 113 will be only partially closed in providingrecycle operation.

The recycle operation above described is particularly useful atextremely low ambient temperatures, wherein the temperature differencebetween ambient temperature and the temperature downstream of theevaporative coil becomes quite low. For example, at temperatures belowabout 30 F., the air circulating across the evaporative coil 106 inonce-through operation may be insuflicient to provide more than anominal amount of heat, considered apart from that heat added by the gasburner. Assuming, for example, that the heat pump is being operated at aheat load of about 35,700 Btu. per hour, with the temperature upstreamof the evaporative coil 106 being maintained at 40 F. by the addition ofextraneous heat from radiator 124, the temperature downstream of thecoil being 28.5 F., and assuming that the ambient temperature is 285, noheat will be abstracted from the ambient air circulating through thehousing. This is so because under the conditions stated, the temperaturedownstream of the evaporative coil is equal to ambient temperature, andno net loss in heat content or enthalpy will be experienced by the airin its passage through the housing. Since the downstream temperaturewill remain at 28.5 if the upstream temperature is maintained at 40 F.,as the ambient temperature drops below 28.5 a net loss of heat to theambient atmosphere will be experienced by reason of the differencebetween the 285 F. discharge temperature and the ambient temperature.Assuming an ambient temperature of 18.5", it will be seen that a 10 F.ditference in temperature between the exhausted air and ambientatmosphere will be suffered and that the heat in the discharged airrepresenting the 10 difference will be a net loss to the system. Underthese conditions, a substantially total recycle of the air within thehousing will limit the heat loss to the atmosphere to that amount of airwhich necessarily must be circulated in order to provide oxygen forcombustion of the heating fuel.

Therefore, it is preferred to operate the heat pump of the presentinvention under substantially total recycle of air within the housing111 when ambient temperature is equal to or below that down-stream ofthe evaporative coil under full load.

Referring now to FIG. 2, there is schematically shown a system wherebyautomatic control of the recycle feature may be controlled by ambienttemperature. In the schematic diagram shown in FIG. 2, the housing 211,similar to housing 111, is provided with valves 213 and 217, similar tothe valves 113 and 117. The valves 213 and 217 are movable between fullyopen positions and a substantially closed position as shown by thedotted lines in the diagram by moving means indicated by the boxes 218and 220. These means 218 and 220 may comprise two position solenoid typemovers or other type two position motors supplied with suitable linkagesin order to move the valves 213 and 217 in the desired manner. Theselinkages may include bell cranks and push rods, ratchets and ratchetgears, etc., all is is well known in the art. The particular linkagesform no part of the present invention. The ambient atmosphere is sensedby a temperature responsive means 222, and upon the ambient temperaturesbecoming lower than the set point, the means 218 and 220 are actuated inorder to move the valves 213 and 217 to the positions shown in the solidlines. As ambient temperature rises above the set point, the movers 213and 220 would move the valves 213 and 217 in the positions shown by thedotted lines. The temperature set point would be related to thetemperature downstream of the evaporative coil 206, under full-loadconditions. It could be this temperature exactly, or 1 or so above thattemperature in order to avoid loss of added heat to the atmosphere. Theheater 232 is controlled by temperature sensitive means 234 whichcontrols the valve 236. It should be understood that a pilot light willbe provided in order to maintain a means for lighting the valve 232should the gas flow be shut off completely by valve 236. The overridemeans 224 positioned in the circulating air duct 205 may be provided toreset the temperature responsive means 234 to a higher temperature,providing a larger temperature difference between the circulating airwithin housing 211 and the liquid within the evaporative coil 206 andthereby increasing the flow of heat into the condensing coil 206 fortransmission into the flowing air within duct 205. Thus, a dual controlsystem is provided which will maintain temperatures within the comfortrange within the building being heated while maintaining a recycle airstream within the duct 211 at ambient temperatures which require thisrecycle stream for optimum efficiency.

It should be noted that the system set forth above is applicable notonly to the split unit type of heat pump as is shown in FIG. 1, but alsoto the combined unit which is contained in a single housing, which wouldmerely mean an adaptation of the heating means to provide heat adjacentthe evaporative coil. It might also be noted that during summertimeoperation, the heating system of the present invention is inactivated,the valve 102 would be rotated in order to change the direction ofcoolant flow, in which case the coil 106 would become the condensingcoil and coil 104 would become the evaporative coil. This would providefor cooling within the building duct 146.

By means of the invention as above set forth, a process for increasingthe efficiency of heat pumps at low ambient temperatures has beenprovided, which comprises supplying additional heat to the air streamupstream of the evaporative coil whereby the apparent ambienttemperature is raised above that actually obtaining. It has been. shownthat by the practice of this process, the capacity of a heat pump may bemaintained near an optimum, and heat losses to the ambient atmosphereare minimized. Accordingly, therefore, the process of increasing theefficiency of a heat pump and the apparatus therefor, as set forthabove, should be limited not by the specific examples given, but ratherby the scope of the appended claim.

I claim:

In a heat pump system comprising a first duct containing a condensingcoil and means passing air thereover, a compressor, an evaporating coil,and means fluidly connecting said compressor, said condensing coil, andsaid evaporating coil for circulation of a refrigerant in a closedsystem, I

the improvement which comprises a housing having an air inlet and an airoutlet,

wall means interiorly dividing said housing into a main duct and arecycle duct, said wall means terminating proximate to said outlet,

said evaporating coil being located in said main duct,

means for circulating air through said main duct and said recycle duct,

heating means in said housing,

first valve means associated with said air inlet and movable to an openposition and a closed position,

second valve means associated with said air outlet and movable to anopen position whereby said recycle duct is closed and said'outlet isopen, and to a closed position whereby said recycle duct is open andsaid outlet is closed,

first temperature sensing means located eXteriorly of said housing,

means responsive to said temperature sensing means to move said firstand second valve means to said closed positions over said air inlet andair outlet thereby opening said recycle duct means at a predeterminedlower ambient temperature, and to said open positions over said airinlet and air outlet thereby closing said recycle duct means at apredetermined higher ambient temperature,

second temperature sensing means in said first duct,

third temperature sensing means in said housing upstream of saidevaporating coil,

and means responsive to both of said second and third sensing means forcontrolling said heating means;

References Cited in the file of this patent UNITED STATES PATENTS1,737,040 Bulkeley et al Nov. 26, 1929 2,124,268 Williams July 19, 19382,209,787 Miller July 30, 1940 2,263,476 Sunday Nov. 18, 1941 2,468,626Graham Apr. 26, 1949 2,799,482 Rawdon July 16, 1959

